1. Field of the Invention
The present invention relates to a novel .alpha.-glycosyl quercetin, and its preparation and uses, more particularly, it relates to (i) an .alpha.-glycosyl quercetin wherein at least equimolar D-glucose residues are attached to quercetin via the .alpha.-bond; (ii) a process for preparing .alpha.-glycosyl quercetin comprising subjecting a solution containing quercetin and an .alpha.-glucosyl saccharide to the action of a saccharide-transferring enzyme to form an .alpha.-glycosyl quercetin; and recoverying the resultant .alpha.-glycosyl quercetin, and (iii) a composition, for example, food products, cosmetics and pharmaceuticals for susceptive diseases, into which said .alpha.-glycosyl quercetin is incorporated.
2. Description of the Prior Art
Usually, quercetin is widely distributed in the plant kingdom as a glycoside, i.e. rutin wherein a saccharide is attached to quercetin via the .beta.-bond, and can be prepared by extracting and separating such a glycoside from plants and hydrolyzing the resultant glycoside with an acid or an enzyme to remove saccharides therefrom.
Quercetin has a relatively-large resonance structure in terms of the chemical structure, and this exhibits a yellow-color-imparting ability, antioxidation activity, vitamin-P activity and ultraviolet-absorbing activity. Thus, quercetin could be useful in the fields of food products, pharmaceuticals and cosmetics.
Quercetin, however, is soluble in a readily water-soluble organic solvent, but insoluble or scarcely soluble in water, and this renders the handleability very difficult.
Propolis is an example of the fact that a large amount of quercetin is present in the natural world. As described in Propolis in natural therapeutics (1983), published by Maloine Editeur S. A., Paris, France, and Fragrance Journal, No. 83, pp. 36-39 (1987), propolis is a resin-like product which is stored by bees in a beehive, said propolis containing resins, beeswaxes, essential oils, pollens and flavonoids, and has been used in a variety of folk medicines for a long time.
Recently, it was found that flavonoids in propolis were mainly composed of flavon aglycons such as chrysin, and flavonol aglycons such as galangin and quercetin, said flavonoids having been noticed as a major effective component of propolis.
The flavonoids are prepared by the extraction of propolis with a readily water-soluble organic solvent such as methanol and ethanol, and an extract prepared in this manner has been commercially available in these days as a propolis extract or a propolis tincture.
The flavonoids, however, dissolve in a water-soluble organic solvent, but are insoluble or scarcely soluble in water, and this strongly restricts their actual use.